Drop Python 3.3, add Python 3.7 and Django 2.1

This is a combination of 5 commits.

Commit message #1:

    Drop support for Python 3.3

    Setuptools and Tox no longer support or work on Python 3.3.

Commit message #2:

    Tox / Travis: Add Python 3.7 and Django 2.1

Commit message #3:

    Tox: Django 2.1 drops support for Python 3.4

Commit message #4:

    Travis: Add workaround for Python 3.7

    Upstream issue: https://github.com/travis-ci/travis-ci/issues/9815

Commit message #5:

    Travis: Enable pip caching

.travis.yml

@@ -1,7 +1,8 @@
 language: python
+cache: pip
+
 python:
   - 2.7
-  - 3.3
   - 3.4
   - 3.5
   - 3.6
@@ -12,22 +13,25 @@ env:
   - DJANGO=1.10
   - DJANGO=1.11
   - DJANGO=2.0
+  - DJANGO=2.1
 matrix:
   exclude:
     # Python/Django combinations that aren't officially supported
     - { python: 3.5, env: DJANGO=1.7 }
     - { python: 3.6, env: DJANGO=1.7 }
     - { python: 3.6, env: DJANGO=1.8 }
-    - { python: 3.3, env: DJANGO=1.9 }
     - { python: 3.6, env: DJANGO=1.9 }
-    - { python: 3.3, env: DJANGO=1.10 }
     - { python: 3.6, env: DJANGO=1.10 }
-    - { python: 3.3, env: DJANGO=1.11 }
     - { python: 2.7, env: DJANGO=2.0 }
-    - { python: 3.3, env: DJANGO=2.0 }
+    - { python: 2.7, env: DJANGO=2.1 }
+    - { python: 3.4, env: DJANGO=2.1 }
   include:
     - { python: 3.6, env: TOXENV=flake8 }
     - { python: 3.6, env: TOXENV=readme }
+    # Work around Travis Python 3.7 issue: https://github.com/travis-ci/travis-ci/issues/9815
+    - { python: 3.7, env: DJANGO=1.11, dist: xenial, sudo: true }
+    - { python: 3.7, env: DJANGO=2.0, dist: xenial, sudo: true }
+    - { python: 3.7, env: DJANGO=2.1, dist: xenial, sudo: true }
 
 install:
   - pip install tox-travis

setup.py

@@ -80,6 +80,7 @@ setup(
         'Framework :: Django :: 1.10',
         'Framework :: Django :: 1.11',
         'Framework :: Django :: 2.0',
+        'Framework :: Django :: 2.1',
         'Intended Audience :: Developers',
         'License :: OSI Approved :: MIT License',
         'Operating System :: OS Independent',
@@ -89,10 +90,10 @@ setup(
         'Programming Language :: Python :: 2',
         'Programming Language :: Python :: 2.7',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.3',
         'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.7',
     ],
     platforms=['any'],
     url='https://github.com/jcassee/django-analytical',

tox.ini

@@ -1,12 +1,13 @@
 [tox]
 envlist =
     # Python/Django combinations that are officially supported
-    py{27,33,34}-django17
-    py{27,33,34,35}-django18
+    py{27,34}-django17
+    py{27,34,35}-django18
     py{27,34,35}-django19
     py{27,34,35}-django110
-    py{27,34,35,36}-django111
-    py{34,35,36}-django20
+    py{27,34,35,36,37}-django111
+    py{34,35,36,37}-django20
+    py{35,36,37}-django21
     flake8
     readme
 
@@ -23,6 +24,7 @@ deps =
     django110: Django>=1.10,<1.11
     django111: Django>=1.11,<2.0
     django20: Django>=2.0,<2.1
+    django21: Django>=2.1,<2.2
 passenv = TRAVIS TRAVIS_JOB_ID TRAVIS_BRANCH
 whitelist_externals = sh
 
@@ -42,6 +44,7 @@ DJANGO =
     1.10: django110
     1.11: django111
     2.0: django20
+    2.1: django21
 
 [flake8]
 max-line-length = 100